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The Precambrian Period
is the longest period in Earth's history. It lasted from the
formation of the Earth about 4.6 billion years ago right up to about
540 million years ago. If Earth's history were changed into a
dollar, the Precambrian Period would be worth about 88 cents!
Birth Of A Double Planet
In the first 800
million years, known as the Hadean Eon, the Earth and Moon
formed to become what many scientists call a double planet. They
are called this because the Earth and Moon are both large enough to be
planets (the Moon is larger than Pluto!) and they are close enough in
space to have one orbit the other. The Earth and Moon
formed through the process of smaller bodies of planet building
material colliding with larger bodies as described in the Nebula
Theory section of the timeline on this site.
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| Two Planets? |
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 The
Earth and Moon formed side by side during the Hadean Eon of the
Precambrian Period. The Hadean Eon gets its name from the greek
god of the underworld, Hades. Why do you think it was named for
this particular god?
(Click
on the image for a closer look.)
Image Credit: NASA
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| Recycling
The Earth |
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 The oceans and
atmosphere formed from water vapor and other gases bubbling out of the
early molten Earth. The water may have come mostly from comet
collisions as the young Earth was forming.
Today,
volcanic activity recycles elements that replenish the Earth's crust,
atmosphere and oceans.
(Click on the image for a closer look.)
Image Credit: USGS
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